qemu: blockjob: Don't leak 'cfg' from qemuBlockJobEventProcessLegacy

Since c2573527 a reference of 'cfg' would be leaked if the function
does not need to process anything. Fix it by using VIR_AUTOUNREF.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_blockjob.c

@@ -315,7 +315,7 @@ qemuBlockJobEventProcessLegacy(virQEMUDriverPtr driver,
                                qemuBlockJobDataPtr job,
                                int asyncJob)
 {
-    virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
+    VIR_AUTOUNREF(virQEMUDriverConfigPtr) cfg = virQEMUDriverGetConfig(driver);
     virDomainDiskDefPtr disk = job->disk;
 
     VIR_DEBUG("disk=%s, mirrorState=%s, type=%d, state=%d, newstate=%d",
@@ -368,8 +368,6 @@ qemuBlockJobEventProcessLegacy(virQEMUDriverPtr driver,
             VIR_WARN("Unable to update persistent definition on vm %s "
                      "after block job", vm->def->name);
     }
-
-    virObjectUnref(cfg);
 }